In "Ode to the West Wind," why does Shelley call the West Wind "destroyer" and "preserver"?
Shelley's "Ode to the West Wind" was written within the Romantic tradition, and utilizes common Romantic tropes such as the personification of Nature and the invocation of pathetic fallacy, wherein Nature has human attributes and motivations. As a great natural power, then, Shelley's "West Wind" is both creative and destructive, a force to which humans are subject.
At the beginning of the poem, Shelley describes the West Wind as the "breath of Autumn's being," suggesting a vibrant and living force which drives away dead things before it—"like ghosts from an enchanter fleeing." In this way, the Wind clears the path for new life to emerge, establishing it as a creative force. It is the Wind which "chariotest [conveys] to their dark wintry bed/the winged seeds." While the seeds will lie "each like a corpse within its grave" until summer, without the strong winds of winter, a space could not have been cleared for them to grow in when the time is right. For this reason, the West Wind can be seen as a "preserver," maintaining the cycle of life and death in nature and preserving the balance.
At the same time, of course, the Wind's destructive properties cannot be forgotten. As the "dirge of the dying year," its song is a symbol that the havoc of winter is about to be wreaked upon the earth, with the Wind generating an atmosphere from which "black rain, hail and fire will burst." While the coming of winter is a necessary part of a cycle of renewal, the West Wind can also have devastating effects upon those who fall prey to its "uncontrollable" whims.
In an apostrophe to the West Wind (apostrophe: addressing someone who is not present or is dead, or something that is not human as though present and living), Shelly is following an established poetic convention of seeking the guidance, inspiration and attention of the muse of the poem, in this case, the muse is the" wild West Wind." Whereas early poets, through to at least the Elizabethan period, believed their divine inspiration for poetry came from God and imparted spiritual truth that humans craved to know, Romantic poets believed their inspiration for poetry came from nature and imparted truth about nature, human nature, and philosophical musings.
Shelly describes the West Wind as something that can be seen only through its force and power, like driving leaves before the wind or blowing seeds to a cold grave. Shelly then turns the topic of the first stanza and speaks of the West Wind's cousin, the Spring wind, that will blow and summons to life the sleeping seeds that will raise "sweet buds" to the air. It is in this context that Shelly calls the West Wind a Wild Spirit that is both a "Destroyer" and a "Preserver": The West Wind destroys the peaceful landscape of autumn by driving life (e.g., seeds, leaves) before it to cold graves, but it is a preserver because it buries, or plants, the seeds of next year's life to be awakened by the Spring wind that blows.